It was Williams' earliest loss at Wimbledon since she exited in the same round in 2005.

"I cannot believe it that I did it myself," Cornet said to BBC TV shortly after kissing the grass on Court 1. "Wow, me!"

Cornet, the 25th seed from France, could barely find her legs when the players returned from a several-hour rain delay locked at 1-1, 40/40.

No. 1 Williams rolled off the next five games.

But the emotive Frenchwoman, her belief growing with every stroke, fired away on returns and groundstokes and mixed in the occasional short ball as an agitated Williams failed to find the form that has earned her 17 Grand Slam titles.

In the next two sets, the 32-year-old American fell behind 5-0 and 5-2, looking tentative and passive and failing to employ the ferocity and power that have marked her career.

She closed to 5-4 in the final set, but an emboldened â?? and soon-to-be ecstatic â?? Cornet served out the final game at love.

"I think everyone in general plays the match of their lives against me," said a sullen Williams afterwards, suggesting that opponents raise their level and swing with nothing to lose "as if they're on the ATP Tour."

"It's never easy, you know, being in my shoes," she added.

Her vaunted serve didn't bail her out, either.

Williams, who hit a Wimbledon record 102 aces on her way to the 2012 crown, fired just three against Cornet while committing seven double faults.

She landed only 66% of her first serves and won just 30% of her second-serve points in the match.

Cornet had already beaten Serena Williams once in 2014 in the semifinals at Dubai. But this was a much bigger stage.

"Well, it's amazing because beating Serena two times in a row, it doesn't happen very often, so I'm glad," said Cornet.

Williams, who won a career-best 11 tournaments last year, including the French Open and U.S Open, has now failed to advance past the fourth round four of her last five majors.

This year, she lost in the fourth round of the Australian Open to Ana Ivanovic and in the second round of the French Open to Garbine Muguruza.

Her coach, Patrick Mouratoglou, said it was evident Williams was not in the right frame of mind when she trailed early in the second set.

"The fact that there is zero reaction is a very big indicator that she's not there at all," he said. "She's pushing the ball, expecting mistakes. She's not going to win like this, I know."

Mouratoglou, who runs an academy outside Paris and teamed up with Williams when she lost in the first round at Roland Garros two years ago, dismissed talk that her opponents had more self-belief, that her serve needed re-tooling or that last year's heavy schedule had taken a toll.

He said she was not in a good "space" and he didn't know why.

"Definitely since January she is not there," he said. "She's not herself. She's an average player if she doesn't have the mindset that she usually has on the court."

Williams, with three titles at Brisbane, Miami and Rome in 2014, had plenty of reasons to be motivated.

Last year eventual finalist Sabine Lisicki ousted her in the fourth round here. Williams is one major from tying Chris Evert and Martina Navratilova, who each have 18 Grand Slam titles in singles.

Williams admitted that reeling in Evert and Navratilova was off the radar because she hadn't been close enough in recent months to feel that kind of pressure.

"I don't think it's been that much on my mind," she said.

Cornet, 24, said she once disliked grass but finally decided to embrace it and improve her forehand, which had been a weakness on the surface.

The Nice native, whose previous best result at a major was reaching the last 16 at the 2009 Australian Open, said she was not intimidated by any player, even Williams, and stuck to the same tactics she had used in Dubai.

"I think maybe she doesn't like so much the way I'm playing," she said. "I'm pretty creative on the court, doing some different things."

While Williams leaves London with plenty of questions and shaken confidence, Cornet hopes to pucker up again if her run continues when she plays No. 13 seed Eugenie Bouchard of Canada next.

Her first smooch of a tennis court was no hollow peck.

"I think it's very symbolic because it means now I love you grass and I didn't before," she said.